1. Field of the Invention
The present invention relates to canisters and, in particular, to canisters that have both of an adsorption material and a heat storage material.
2. Description of the Related Art
Typically, this kind of canister is disposed at a midpoint of a path communicating between a fuel tank of a vehicle and an outside of the fuel tank. When the vehicle is stopped, fuel vapor produced within the fuel tank is introduced into the canister, where a fuel component, such as butane, is removed (adsorbed) from the fuel vapor, and the remaining air component (oxygen and nitrogen) having a relatively small molecular diameter is discharged to the outside. The adsorbed fuel component can be desorbed by the flow of the outside air that is introduced into the canister during driving of the vehicle and the desorbed fuel component may then be purged into a vehicle engine.
An adsorption material, such as activated carbon, is disposed within the canister. The adsorption material may have properties of adsorbing a fuel component by an exothermic reaction and desorbing the fuel component by an endothermic reaction. Therefore, as the temperature of the canister increases due to adsorption of the fuel vapor, the adsorption performance of the canister (i.e., an adsorption ability of the adsorption material) may be lowered. On the other hand, as the temperature of the canister decreases due to desorption of the fuel vapor, the desorption performance of the canister (i.e., a desorption ability of the adsorption material) may be lowered.
Japanese Laid-Open Patent Publication No. 2005-233106 has proposed a canister having a heat storage material contained within the canister in addition to an adsorption material. Therefore, temperature variation that may be caused due to absorption and dissipation of heat by the adsorption material may be adjusted by the heat storage material, so that the adsorption and desorption performances can be properly maintained. The heat storage material is in forms of granules that are formed by granulating a mixture of a plurality of capsules and a binder. Each of the capsules is made of a melamine resin and sealingly contains a phase change material (such as n-eicosane) that can absorb or dissipate latent heat in response to the temperature within the canister. It may be preferable that the phase change material can rapidly change its phase in response to change in temperature within the canister. Therefore, typically, a granulation process of the capsules is performed by using a minimum amount of the binder in order to prevent the capsules from being covered by the binder. (More specifically, spaces or voids are provided between the capsules for exposing the capsules.)
In recent years, as alternative fuel of gasoline, alcohol-containing fuel (such as ethanol-containing fuel) has been used in various vehicles. Also in the case of using such alternative, it may be still appropriate to provide a canister at a midpoint of a path for discharging fuel vapor (alcohol vapor) to the outside. However, if the canister disclosed in the above Publication No. 2005-233106 is used for this purpose, the adsorption and desorption performances may be extremely lowered in some cases.
The inventors of the present invention devoted to prove the cause of reduction in performance of the canister and found that a main reason of reduction in performance is that alcoholic vapor enters the heat storage material (the exposed capsules) to cause the phase change material to flow out of the heat storage material.
Therefore, there is a need in the art for canisters having a heat storage material that can prevent or minimize outflow of a phase change material from the heat storage material, which may be caused by alcoholic vapor.